1. Field of the Invention
The invention relates to nondestructive evaluation of non-living test samples, also referred to as industrial NDE, by reflected waveform scanning: for example ultrasound or eddy current NDE scanning. The scanning probe includes a self-contained multi-axis position encoder that correlates both multi-dimensional probe underside translation and rotation motion across the test sample surface with the multi-dimensional spatial location on the test object surface. The position encoder compensates for probe rotation that would otherwise negatively impact probe position determination accuracy.
2. Description of the Prior Art
Ultrasound and eddy current industrial NDE scanners transmit penetrating waveforms into an inanimate test object sample and capture the reflected waveform. The reflective waveform data are analyzed to extract information about internal characteristics of the test object, including by way of nonlimiting example sample thickness and other internal dimensions, internal non-homogeneities, such as cracks or voids and density variations.
NDE of an industrial object by an eddy current modality identifies discontinuities, such as cracks or voids, by passage of a steady state alternating current or pulsed current waveform in a test probe transmitter coil that is electromagnetically coupled in close proximity to an electrically conductive test object. The changing current flow in the probe transmitter generates a changing transmitted magnetic field waveform that in turn induces a generated eddy current in the electromagnetically coupled test object. Variations in the phase and magnitude of these generated eddy currents within the test object create a responsive or reflected magnetic field waveform that is in turn sensed by a test probe receiver coil as an induced received or reflected current flow. In some known eddy current NDE systems the test probe's transmitter coil also functions as the receiver coil. Thus, variations in the electrical conductivity or magnetic permeability of the test object, or the presence of any flaws, will cause a change in eddy current and a corresponding change in the phase and amplitude of the reflected magnetic waveform as sensed by the test probe receiver changes in its current waveform. Amplitude and intensity of an eddy current within a test object will stay substantially constant if its magnetic transmission characteristics (which impact the reflected waveform) are substantially constant. However, anomalies in the test object alter its magnetic transmission characteristics at the anomaly location. Accordingly, anomalies and their spatial location within the test object can be detected by determining if the magnetic transmission characteristics of the material being scanned are consistent with the presence or absence of an anomaly at each scan spatial location.
NDE of an industrial object by an ultrasonic modality identifies discontinuities, such as cracks or voids, by transmission of pulsed sound waves through the object and reception of reflected “echo” waveforms. Often pulse transmission and echo reception are performed by a probe device. The reflected waveform is analyzed for acoustic patterns that are correlated with discontinuities in the inspected test object sample. A discontinuity present in a given material will reflect a different waveform than discontinuity-free homogeneous material. Generally, relative distance between the ultrasonic probe and the discontinuity is a function of elapsed time between probe transmission of the sound wave and reception of the reflected waveform. Discontinuity physical size (i.e., its occupied volume) is indirectly correlated with the echo waveform energy (e.g., amplitude), because reflected energy is impacted by a multitude of physical factors including discontinuity physical size and dimensions, as well as attenuation of the wave energy as it travels through the inspected material.
Reflected or “echo” wave amplitude alone from a single waveform scan orientation may not provide sufficient information to determine the estimated envelope of physical dimensions and profile of a discontinuity. Dimensional and profile information is useful for making an ultimate inspection determination whether the inspected part is acceptable to use in industrial service. In the past, analysis of a plurality reflected waveforms taken from different respective probe scan positions about the inspected object and variation of transmitted wave frequency/wavelength has enabled inspectors to construct composite spectral and/or visual images of a scanned object that correlate the approximate discontinuity size with that of a known hole size or a plurality of adjoining holes. Depending upon the physical dimensions of the scanned inanimate object and the relative dimensions of discontinuities, ultrasonic images have been constructed of sufficient resolution evaluate potential impact on the inspected part's future use in service.
Referring to FIG. 1, current technology for manual ultrasonic and eddy current inspection in industrial nondestructive testing modalities are limited to a single scanning axis, with the volume of test object sample or specimen 20 scanning limited by the probe's effective scan width along a scanned surface 22. Existing ultrasonic or eddy current NDE inspection test apparatuses 30 include an NDE controller 31 and a test probe 32 which are coupled by power and data cable 33. At a given test probe 32 spatial position on the surface 22 (e.g., position I) the probe transmits penetrating waves into the test sample top surface 22 and receives the reflected waveform data relevant to that spatial position. Using a test probe motion control system 34 and/or a test object motion control system 36 under general control by the NDE controller 31 (issuing motion control commands MC), the probe 32 is translated to other positions II-N along the X axis path, and waveform data are gathered for each of those positions. The motion control systems can be affixed to the probe or test sample so that all relative probe/test object positioning is controlled by those systems. Alternatively a free-hand probe that is not coupled to a probe motion control system can be moved along a controlled path across a test object by abutting the probe against a pre-positioned fixture of known coordinate location relative to the test object—analogous to abutting a pencil against a ruler to draw a straight line at a desired known position on a sheet of paper. Upon motion of the probe across the pre-defined translation path, a scan data set, matching spatial position data with the waveform data, are sent to the NDE analyzer 38 for transforming the scan data set into spatially mapped internal structural characterizations of the test object, e.g., voids, cracks, discontinuities, etc. The characterization information may be extracted for analysis via human machine interface (HMI) 39 or forwarded to other analysis or data storage devices for further processing.
Known NDE inspection systems 30 employ probe positioning motion control systems 34/36 with single wheel encoders and/or retractable line encoders, which are limited to single-dimensional line scans of test samples that correlate the motion control position across a line scanning path with waveform readings, such as the X axis path shown in FIG. 1. Due to the single-line scanning limitation, the scanner 30 evaluation of the test object 20 volume is limited to the probe 32 corresponding effective scanning width. When a larger volume of the test object 20 needs to be scanned the motion control system 34/36 follows a rastered path, which in the example of FIG. 1 moves the probe 32 and/or test object 20 to a different position on the motion control system 34 and/or 36 single wheel encoded orthogonal Y axis to complete another scan line across the X axis. As the motion control system 34/36 is incapable of free-hand multi-axis scanning, compliance with raster scan coordinate data gathering is required (i.e., some combination of controlled X and Y motions to gather accurate probe positional spatial data). Any deviation from the path predefined rastered pathways can lead to inaccurate correlation of scan data and spatial position. Also failure to follow organized rastered scanning protocols can lead to “gaps” in the acquired data scan sets, in which portions of the test object volume structure are not properly characterized.
While organized rastered scanning under motion control system positioning control facilitates NDE scanning of an entire test object volume, in some applications it may not be practical to transport a test object to an inspection site having a motion controlled NDE inspection system. Conversely, test object location or site limitations may also make it impractical to transport a motion-controlled NDE scanning system to the test object's field site.
Use of a full motion-controlled NDE scanning system may not be practical or convenient to conduct a limited local scan of only a portion of a test object in the field, where flexible or spontaneous use of a hand-held scanning probe system might be helpful for field service. Unfortunately, with present NDE scanning systems hand-held or free-hand scanning probe manipulation is not practical because spatial position and waveform data cannot be correlated accurately for NDE analyzer analysis of a test sample volume greater than an accessible at a single probe spatial position.
Thus, a need exists in the art for a waveform eddy current or ultrasound modality NDE system that can perform a multi-dimensional scan of a test object sample without use of a probe positioning motion control system, while maintaining NDE accuracy.
A need also exists in the art for a waveform eddy current or ultrasound modality NDE system that can perform a multi-dimensional scan of a test object sample with a hand-held scanning probe that is capable of selective free-hand, multi-dimensional spatial positioning by an operator, while maintaining NDE accuracy.